In recent years, the market of interchangeable-lens type camera systems (also referred to simply as “camera systems”, hereinafter) have been spreading rapidly. Such an interchangeable-lens type camera system includes: a camera body having an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor); and an interchangeable lens apparatus having a zoom lens system for forming an optical image on a light receiving surface of the image sensor. An image sensor included in the interchangeable-lens type camera system is larger in scale than that included in a compact digital camera. Accordingly, the interchangeable-lens type camera system can shoot a high-sensitivity and high-quality image. Further, the interchangeable-lens type camera system is advantageous in that a focusing operation and image processing after shooting can be performed at a high speed, and that an interchangeable lens apparatus can be easily replaced in accordance with a scene that a user desires to shoot. An interchangeable lens apparatus having a zoom lens system capable of forming an optical image with variable magnification is popular because such an interchangeable lens apparatus can freely vary the focal length without lens replacement.